


Donnie's Favorite Test Subject

by GamerGirl140



Series: Our Own Magic universe [3]
Category: Rise of the Teenage Mutant Ninja Turtles (Cartoon 2018), Teenage Mutant Ninja Turtles - All Media Types
Genre: Anal Sex, Body Worship, Bondage, Handcuffs, Kissing, M/M, Not Actually Unrequited Love, Perverted Use for Mystic Powers, Post-Season 2, Sex Toys, Sexual Roleplay, True Love, Turtlecest (TMNT), Unrequited Love
Language: English
Status: Completed
Published: 2020-12-29
Updated: 2020-12-29
Packaged: 2021-03-10 18:55:14
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,574
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28412001
Author URL: https://archiveofourown.org/users/GamerGirl140/pseuds/GamerGirl140
Summary: After a finding something rather interesting by chance, Donnie is ready to test it out. Luckily, he knows who the perfect test subject is.
Relationships: Donatello/Leonardo (TMNT)
Series: Our Own Magic universe [3]
Series URL: https://archiveofourown.org/series/2068815
Comments: 7
Kudos: 22





	Donnie's Favorite Test Subject

On an ordinary evening in the Hamatos’ sewer lair, one Donatello was holed up in his lab/room preparing for something. He meticulously went over every last thing necessary for tonight’s events several times before finally being satisfied with the current results. Everything was set, it was time to bring HIM in.

In a previous adventure Donnie went on with his three brothers, the group happened upon a strange mystic device. Naturally, Donnie took an interest in it and took it back home for further examination. In his examinations, he discovered that the device was in fact, a mystic sex toy. And Donnie had a few ideas as to what to do with the device. Amazing, genius ideas.

Leonardo, Donnie’s older twin brother and the love of his life, was the only other one who knew about the true nature of the device. As Donnie had told him about it one night after getting completely _ravished_ by him. While Leo didn’t know exactly what the device did, he did volunteer to let Donnie use it on him. And today, Donnie fully intended to take advantage of his mate’s offer. Having finished with his preparations, Donnie sent a text to Leo, telling him that he wanted to see him.

“Ah, Nardo, just the turtle I wanted to see,” Donnie announced when Leo made his way into the softshell’s lab. The slider then greeted his mate with a kiss on his cheek before walking over to an area of the lab that the pair considered their playroom. The room had a bed, a table and a few chests and dressers, all filled with things the pair would need if they felt like getting kinky, as opposed to the love nest which they reserved for more romantic encounters.

“So, what’s this all about?” Leo wondered as Donnie followed him into the playroom, which was hidden behind a thick, black curtain.

“Remember that mystic device we found not too long ago?” Donnie asked as he opened a drawer in the dresser and pulled something out of it.

“You mean the device you told me was a sex toy? Are you ready to test it out?” Leo asked, not paying attention to what Donnie was doing.

“About that…I had something special in mind for that. If you don’t mind playing a game of sorts…” Donnie explained, suddenly feeling nervous. Donnie’s sudden change in tone got Leo’s attention.

“Donnie, baby, you know I don’t mind playing your ‘games.’ In fact, you know I love them,” Leo said reassuringly, while wrapping his arms around Donnie’s waist from behind and nuzzling his cheek.

“It’s still surprising to me is all,” Donnie explained, while leaning back into Leo’s embrace.

“What can I say, being the leader is unbelievably stressful and sometimes it’s nice not being in charge,” Leo responded, tightening his embrace, and planting a kiss on Donnie’s cheek. “So, what did you have in mind?” Leo asked.

“Why not use your mystic powers to figure it out instead,” Donnie suggested with a smirk. Leo clicked his tongue in playful irritation before closing his eyes and focusing. By drawing on the magic within him, he was able to look into Donnie’s mind. Almost immediately, Leo got a glimpse of what Donnie wanted to do with him. Donnie could feel Leo shiver in response to reading that thought.

“I love it! Let’s do it!” Leo declared, before turning Donnie’s head to give him a proper kiss, which Donnie eagerly returned.

“Then strip down and get on the bed. I’ll be there shortly,” Donnie said as Leo released him from his grasp. Leo then stripped off all his gear and dropped it in a bin on top of the dresser while Donnie disappeared behind a curtain, a different curtain than the one that separated the playroom from the lab. Once Leo was completely bare, he did as he was told by climbing onto the bed, lying on his back, and waiting for Donnie.

Not too long after, Donnie came back wearing only a lab coat and holding a shoe box. He set the shoe box down on the dresser and then turned around to face Leo, holding a pair of handcuffs.

“Now, before we begin, I need to be absolutely sure. Are you okay with doing this?” Donnie asked as he approached the bed.

“Donnie, I trust you with my life and I’m excited to see where this particular game goes. I’m more than okay with doing this,” Leo said reassuringly, making sure to meet Donnie’s gaze in the process. Donnie stopped in his tracks and smiled adoringly at his mate. The magical embers in his heart that represented his bond with Leo had started to grow into a proper fire at Leo’s words. No doubt Leo was experiencing that feeling as well.

“All right, but just in case, do you remember the safeword?” Donnie asked as he reached the bed, ready to handcuff Leo to the headboard.

“I remember, it’s ‘beach ball’, now let’s do this thing!” Leo said excitedly, ready to get to the action. Donnie couldn’t help but chuckle at Leo’s enthusiasm but went about handcuffing Leo with the chain of the cuffs being wrapped behind a post in the headboard. Leo then gave an experimental pull, satisfied by the strength of the cuff chain and the headboard post.

“Are the cuffs too tight or anything?” Donnie asked, making sure all his bases were covered before he got into character.

“Nope, just right,” Leo answered, giving a thumbs-up for emphasis, before turning his focus to getting into character. Donnie nodded in acknowledgement before going back to the box, grabbing a clipboard and another item that Leo couldn’t see. Donnie turned back around and approached Leo, with a stern look on his face and both hands gripping the clipboard.

“Now what do we have here?” Donnie asked in a rather clinical manner, while looking over Leo’s body.

“Someone you caught by mistake and will let go?” Leo responded with genuine-sounding fake nervousness.

“Cute, but wrong. What we have here, is the perfect subject for my latest experiment,” Donnie explained in the same clinical tone. As he said this, he briefly cupped Leo’s cheek, rubbing his thumb across the bottom half of a red marking on his face before sliding that hand down Leo’s body, making sure to run his fingers across Leo’s slit and finishing by gripping his tail in a pinch grip and running said grip down the whole length of it. The way Leo’s breath hitched, and the way he squirmed in response to the sensual touches was quite gratifying to Donnie. If Leo’s enthusiasm hadn’t given him more confidence about going through with this, then Leo’s reactions did.

“What…what are you gonna do to me?” Leo asked, feigning apprehension. Donnie had to admit, if he wasn’t already aware that Leo was simply playing a role as part of their game, then his tone would have been cause for concern. He would have to remember to reward him for a convincing performance.

“Now, now, you have absolutely nothing to worry about,” Donnie said as he put the clipboard down. On top of the clipboard was a device that Leo recognized, the mystic sex toy they found. “In fact, I can guarantee that you will feel absolutely incredible once the experiment is over,” he said with a smirk that made Leo shiver.

“Why…why me though? What makes me perfect for this?” Leo asked with the same fake nervousness, working hard to sell the performance.

“Why you? Well, your body is what makes you perfect for this, of course,” Donnie responded, the clinical tone from before being gradually replaced by a lust-filled one. He cupped Leo’s face in both hands, directing the slider to look at him. “Your stunning face with these beautiful red markings,” Donnie begins, rubbing his thumbs over Leo’s red facial markings for emphasis. “Your perfect, kissable lips,” Donnie ran a thumb over Leo’s lips before giving him a quick kiss. “Your lovely neck and shoulders,” Donnie’s hands trail down to rub over Leo’s neck and shoulders. “Your strong, powerful arms,” Donnie’s hands start at Leo’s confined wrists and stroke their way down, pausing to rub his biceps for a moment. “Your gorgeous plastron,” Donnie’s hands run over Leo’s plastron, tracing over the grooves between the scutes in the process. “Your shapely, supple legs,” Donnie spends quite a bit of time rubbing Leo’s legs. “Your cute little tail,” Donnie took Leo’s tail into his grasp and stroked it, making Leo squirm deliciously in response. “And with the rest of your body being as perfect as it is, there’s no doubt in my mind that your cock is just as perfect,” Donnie said in a low, desire-filled tone before kissing the bulge beginning to form in Leo’s lower plastron, earning a churr from Leo.

“Thanks…I think,” Leo said, feigning confusion but genuinely appreciating Donnie complimenting his body like this. He’d have to return the favor next time.

“I meant every word. But enough talk, it’s time for the experiment to begin,” Donnie said with a chuckle as he picked up the device. It looked like a small metal rod with numerous markings covering it. Donnie fiddled with it for a moment before two hands and a small spaghetti noodle-thin rod, all made from green mystic hard light, flew out of the rod.

“Just relax, and let the device work its magic,” Donnie said in a soothing tone as the hard light hands and rod flew over to Leo, hovering over his groin. One hand gripped Leo’s tail, the other cupped his concealed erection and the rod carefully inserted itself into Leo’s entrance. Once the rod was fully inside him, Leo felt it squirt out a thick liquid and grow thicker. It rotated several times, completely coating his insides in the liquid, which Leo could only guess was lube.

“All right, everything’s in place. Let’s begin,” Donnie said before closing his eyes and focusing. Leo watched as the rod Donnie was holding became engulfed in a purple light. The hands (and presumably the rod currently inside Leo) also turned purple. Their shape changed as well. The hands before had been five-fingered hands but changed to three-fingered hands like they and their brothers had. The rod changed as well, turning from a simple thick rod into a shape Leo was very familiar with, the shape of Donnie’s penis. The hands also felt as though it was Donnie himself touching Leo.

Once the mystic constructs changed their shape, they got to work. The hand on Leo’s tail began stroking it while the hand on his bulging slit began rubbing it. These motions alone got Leo squirming and moaning in pleasure, but he began straight-up writhing when the rod, well dildo now, inside him began thrusting, hitting his sweet spot with every thrust. Donnie watched hungrily as his mate churred, panted, moaned, and threw his head back into the pillows as the pleasure coursing through his body overwhelmed him. The cuffs chaining him to the bed were the only thing that kept him in place. 

“You love this, don’t you?” Donnie asked, trying but failing to mask his growing desire and feeling his penis begin to stir to life under his plastron.

“YES! I…ah…I do!” Leo answered enthusiastically, focusing on holding his quickly growing erection back, even though it was getting painful.

“I thought so. You look amazing by the way. Beautiful. Enticing. Delicious. Fucking magnificent. And you’re all mine,” Donnie said possessively, no longer bothering to hide his growing lust. Though Leo tried to hold out as long as he could, the pleasure became too much and his penis emerged from hiding, standing proud and hard and wet with precum.

“I was right…your cock is fucking gorgeous,” Donnie said reverently. He’d seen Leo’s penis many times, touched it, sucked it, even took it into his own body, but he treasured every time he’d done so, especially knowing he was the only one with the right to do so. As the magical flames in his heart burned hotter, Donnie quickly approached Leo, still holding onto the control rod. The mystic hand that had been rubbing Leo’s bulging slit was now gripping his shaft, waiting for the next command. Donnie climbed up onto the bed and over Leo so that his face was hovering over his mate’s cock. He stared at it hungrily, licking his lips at the sight of it.

“Smells so good, bet it tastes even better,” Donnie said to no one in particular before pressing a kiss to the tip and running his tongue over it, making Leo cry out in pleasure abruptly. In response, Donnie then took the tip into his mouth, while using the rod to make the mystic hand already gripping Leo’s penis start stroking it. Leo threw his head back into the pillows once again and moaned loudly, louder than before. Donnie braced himself by gripping Leo’s thighs, rubbing them as he continued lavishing the tip of the cock in front of him with loving attention, earning some delicious churrs from his lover.

“I’m…I’m…ahhh…” Leo cried out, trying to let Donnie know that he was on the verge of climax. In response, Donnie doubled his efforts: sucking and licking even harder and making the mystic construct hand speed up its stroking. A mystic construct dildo inside him that felt just like Donnie’s penis, hand on his tail, hand stroking him, Donnie’s mouth on his tip, it was all too much for Leo as he climaxed right into Donnie’s mouth with a loud cry. Donnie paused in his motions, focusing on swallowing Leo’s cum as it entered his mouth. As soon as the flow stopped, Donnie deactivated the device, making the mystic construct hands and dildo vanish.

“Good job, very good job, but we’re not done yet. I still have a need that must be met,” Donnie said as he sat up and licked his lips. He then removed his lab coat and crawled off the bed to both put the device away and grab some special pillows from another chest, putting them behind Leo’s head to prop it up a little more. Once Leo was in a position he liked, he crawled back onto the bed, positioning himself so that his bulge was right in front of Leo’s face.

“Be a good boy and give him a little encouragement,” Donnie ordered as he braced himself by gripping the headboard. Leo took a moment to inhale the amazing scent coming off of Donnie before covering Donnie’s bulging slit with his mouth. Leo ran his tongue over the slit before sticking it in as far as it would go, then flicking it over Donnie’s hardening penis.

“Good boy…good boy…keep going…” Donnie moaned as Leo made out with his slit. He removed one hand from the headboard and pressed it against the back of Leo’s head to keep him there, making sure not to press too hard. As he continued to lavish Donnie’s slit with attention, Leo could feel himself getting hard once again. Not a moment too soon, Donnie felt he was at his limit and pulled back just in time to drop down right in front of Leo’s face. Without prompting, Leo took the tip into his mouth and sucked on it, drawing a churr from Donnie.

“It’s time for the final stage,” Donnie breathed out as he reluctantly pulled away. After grabbing something from the table that Leo couldn’t see, Donnie slid down Leo’s body until they were face to face. He then leaned in and kissed Leo with everything he had, a kiss Leo eagerly returned. While Leo was distracted, Donnie took the key he grabbed and unlocked Leo’s handcuffs, freeing his arms.

“Once I’m inside you, I want you to hold onto me. And don’t let go until I say so. Understood?” Donnie ordered after pulling back from the kiss and positioning the tip of his penis at Leo’s entrance. Leo simply nodded in compliance, spreading his legs wider. Once Donnie had gotten the tip inside, he leaned over Leo before suddenly thrusting the rest into Leo’s tight warmth. Leo did as he was told and wrapped his arms around Donnie’s shoulders while waiting for Donnie to get started. At once, Donnie began thrusting, having angled himself to hit Leo’s sweet spot with each thrust.

“It’s good…so…good…” Leo moaned, throwing his head back and letting the pleasure overtake him. Donnie looked over Leo and liked what he saw. Flushed face, mouth partially open, eyes scrunched shut in pleasure, and almost painfully hard and dripping cock combined made for a truly enticing sight. Donnie churred and quickened his pace.

“And here…I…thought you…c-couldn’t get…any…more beautiful,” Donnie managed to get out before diving in for a kiss. Leo tightened his embrace and eagerly returned his mate’s kiss, entangling their tongues together.

“Donnie…I’m…I’m…” Leo couldn’t quite finish his sentence before a loud moan, followed by a churr forced its way out. Donnie still got the message.

“Don’t come until I say so,” Donnie ordered, stopping his thrusting to get the order out all at once. Leo nodded in compliance and Donnie resumed his thrusting, so very close to reaching his own climax. Mere seconds later, Donnie peaked and shot his load into Leo.

“Please…I need…” Leo begged, coming very close upon feeling Donnie releasing himself inside him.

“Go ahead. You’ve more than earned it for being such a good boy,” Donnie said, still in the middle of his orgasm. At that moment, Leo came as well, covering both their plastrons in his ejaculate. The pair held still for a moment, letting their orgasms subside.

“You can let go now; we need to clean up. Also, the game is now finished,” Donnie said as soon as he was lucid again. Leo released his embrace and his arms fell to his sides, utterly boneless and exhausted. Donnie somehow mustered up the energy to grab some wipes and tissues from a drawer and the two of them took a moment to clean themselves up. Donnie also grabbed a pair of water bottles from a mini fridge in the room and handed one to Leo.

“Thank you,” Leo said softly before opening the water bottle and downing some of it.

“I should be the one thanking you. For letting me do this, that is,” Donnie said bashfully as he sat down next to Leo on the bed.

“It was no problem at all. You were amazing, it was hot, and I loved it,” Leo said reassuringly, taking another drink of water before setting the bottle on the table and getting rid of the extra pillows so he could lay down properly.

“I meant what I said by the way. The compliments I gave you during our game,” Donnie admitted before downing some of his own water.

“I know you did. I’ll just have to return the favor when I’m in charge of one these games,” Leo said with a smirk, turning onto his side. Donnie sat his water down on a nightstand on his side of the bed before finally laying down himself, facing Leo. Leo gazed at him lovingly, making his heart flutter.

“How are you feeling now?” Donnie asked, taking Leo’s wrists into his hand, and gently rubbing them.

“Sleepy…wanna sleep,” Leo said as he started drifting off.

“Go ahead, I’ll be here when you wake up,” Donnie said before taking Leo into his embrace. Leo happily accepted, wrapping his arms around Donnie, and snuggling into his shoulder. Donnie wrapped one arm around Leo’s shoulders while placing the other hand on the back of his head comfortingly.

_He looks so cute when he’s asleep_ , Donnie thought to himself before closing his eyes in contentment.

Unbeknownst to the pair, the entire time they had had an audience. Oldest brother Raphael had come in looking to ask Donnie something and after noticing he and Leo were going at it, stayed to watch, unable to move. He was quite grateful that neither of them noticed him.

Once the pair had finished and fallen into their rest, Raph finally found the will to leave, feeling sad, a little jealous and guilty. The guilt came from eavesdropping on a private, intimate moment that his little brothers were sharing. The jealousy came from his desire to experience a moment like that for himself. The sadness came from the fact that he harbored feelings for his youngest brother Michelangelo that he was certain were unrequited.

Raph wasn’t the only member of the audience though. Up in the vents, in an attempt to memorize their layout, was Mikey. One grate happened to be right above Donnie and Leo’s playroom and Mikey had gotten curious after hearing them in the middle of their game. Much like his big brother, he couldn’t find the will to leave, entranced by what they were doing and grateful that he wasn’t heard or noticed.

After Donnie and Leo had finished and were now resting, Mikey finally found the will to leave, also feeling sad, a little jealous and guilty, for the same reasons as Raph. He desired Raph in the same way Leo and Donnie desired each other but felt certain that Raph didn’t feel the same way.

But a guy can dream, right?

**Author's Note:**

> This is a direct sequel to Our Own Magic. The Perfect Christmas Gift comes right after in the series page because I wanted to get that piece out in time for Christmas. This also draws on my personal headcanons for RotTMNT. I have a list of them in a Google document right here: https://docs.google.com/document/d/1PoX5db_Ft7fZaL0QAFcHmGVY5WbgfUnvzwvZ9cG4l_4/edit?usp=sharing
> 
> You're free to use these headcanons if you want, just be sure to credit me if you do.
> 
> Anyway, hope you enjoy this read. Kudos and bookmarks are great but comments are better.


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